The Aid of Optical Studies in Understanding Millisecond Pulsar Binaries

TL;DR

This paper explores how optical and X-ray observations of millisecond pulsar binaries, especially black widows and redbacks, can reveal details about their shock geometry, emission mechanisms, and pulsar wind physics.

Contribution

It introduces a model linking relativistic Doppler-boosted X-ray light curves to shock geometry, aiding interpretation of observational data in pulsar binaries.

Findings

Simulated double-peaked X-ray light curves match observed patterns.

Redbacks and transitional systems have different shock geometries.

Optical observations can constrain emission geometry and pulsar wind physics.

Abstract

A large number of new "black widow" and "redback" energetic millisecond pulsars with irradiated stellar companions have been discovered through radio and optical searches of unidentified \textit{Fermi} sources. Synchrotron emission, from particles accelerated up to several TeV in the intrabinary shock, exhibits modulation at the binary orbital period. Our simulated double-peaked X-ray light curves modulated at the orbital period, produced by relativistic Doppler-boosting along the intrabinary shock, are found to qualitatively match those observed in many sources. In this model, redbacks and transitional pulsar systems where the double-peaked X-ray light curve is observed at inferior conjunction have intrinsically different shock geometry than other millisecond pulsar binaries where the light curve is centered at superior conjunction. We discuss, and advocate, how current and future optical observations may aid in constraining the emission geometry, intrabinary shock and the unknown physics of pulsar winds.